Enabling SSI Via htaccess

Many people want to use SSI, but don't seem to have the ability to do so
with their current web host. You can change that with htaccess. A note of
caution first...definitely ask permission from your host before you do
this, it can be considered 'hacking' or violation of your host's TOS, so
be safe rather than sorry:

The first line tells the server that pages with a .shtml extension (for
Server parsed HTML) are valid. The second line adds a handler, the actual
SSI bit, in all files named .shtml. This tells the server that any file
named .shtml should be parsed for server side commands. The last line is
just techno-junk that you should throw in there.

And that's it, you should have SSI enabled. But wait...don't feel like
renaming all of your pages to .shtml in order to take advantage of this
neat little toy? Me either! Just add this line to the fragment above,
between the first and second lines:

AddHandler server-parsed .html

A note of caution on that one too, however. This will force the server
to parse every page named .html for SSI commands, even if they have no SSI
commands within them. If you are using SSI sparingly on your site, this is
going to give you more server drain than you can justify. SSI does slow
down a server because it does extra stuff before serving up a page,
although in human terms of speed, it is virtually transparent. Some people
also prefer to allow SSI in html pages so as to avoid letting anyone who
looks at the page extension to know that they are using SSI in order to
prevent the server being compromised through SSI hacks, which is possible.
Either way, you now have the knowledge to use it either way.

If, however, you are going to keep SSI pages with the extension of
.shtml, and you want to use SSI on your Index pages, you need to add the
following line to your htaccess:

DirectoryIndex index.shtml index.html

This allows a page named index.shtml to be your default page, and if
that is not found, index.html is loaded. More on DirectoryIndex later.